Pancreatic islet transplantation is a potential cure for Type I diabetes, a disease which afflicts nearly 2 million persons in the United States, making it the second most common chronic disease in young people. A major challenge is the protection of the marginal islet cell mass. Within a short period after transplantation, inflammatory responses occur in and around the islet grafts, causing early graft failure. Therefore, reducing early inflammation should reduce cell loss and preserve islet cell mass and function. Toll-like receptors (TLRs) recognize pathogen- associated molecular patterns. Ligation via TLRs leads to upregulation of proinflammatory cytokines and chemokines. Islet cells are among the non-immune cells that express functional TLRs. We hypothesize that pre- and posttransplant events produce intrinsic TLR ligands. Islets detect these ligands locally through TLRs and participate in the regulation of immune responses. To test this we propose the following Aims: Aim 1-Determine the impact of Toll-like receptor expression and function on islet cells and their survival. In a syngeneic transplant model we will i) directly assess the role of TLR2 on islet cell survival following prolonged culture;ii) test the relevance of TLR2 expression on parenchymal or bone marrow-derived cells in this process;iii) determine the effect of pre-transplant TLR2 stimulation on the induced adaptive immune response;iv) confirm and define the specificity of TLR activation by analyzing islet-expressed TLRS, TLR4 and TLR9;v) assess mechanisms and potential mediators using a candidate gene analysis approach. Aim 2-Determine the role of islet cell-associated Toll-like receptor engagement in the alloimmune response and tolerance. In an allogeneic transplant model we will i) test the impact of TLR2 and TLR4 engagement on islet allograft rejection;ii) determine the impact of islet TLR2 and TLR4 expression on costimulatory blockade-mediated permanent islet allograft acceptance. Our studies will determine the contribution of the innate and adaptive immune response by focusing on TLRs. A detailed understanding of their role in islet recovery and transplantation may provide new therapeutic approaches in islet transplantation without toxic effects on islet cells and without compromising the whole immune system.